1. Field of the Invention
The present invention relates to a vehicle control system for a motor vehicle (vehicle powered by an internal combustion engine) having a battery which supplies power for engine starting and is charged by electrical power from an engine-driven generator, the vehicle control system including an automatic engine control apparatus having an automatic engine stop/restart control function which is selectively enabled and disabled based on an estimated condition of charge of the battery, and also including a battery charging control apparatus which operates based on that estimated charge condition.
2. Description of Related Art
It is known to maintain the amount of charge stored in a vehicle battery within a predetermined range, in order to extend the operating life of the battery by ensuring that the battery does not become overcharged or excessively discharged. In recent years, an automatic engine stop control function has come into use for motor vehicles whereby the vehicle engine is automatically stopped when certain predetermined conditions exist (typically, when the engine is idling and the vehicle is halted), and whereby the engine is automatically restarted when some other predetermined condition occurs. Fuel consumption and exhaust gas emissions can thereby be reduced.
During such an automatic engine stop/restart operation (sometimes referred to as an “idling stop”), while the engine is stopped, power is supplied from the battery to electrical loads (various equipment of the vehicle). The amount of charge held in the battery is thereby reduced during the interval in which the engine is stopped. Furthermore during each engine restart, a high level of power is supplied from the battery to drive the starter motor, so that the amount of charge in the battery is further reduced. Hence, when such engine to stop/restart operations are repetitively performed, the amount of charge stored in the battery may become excessively low.
For that reason it has been proposed to provide a vehicle control system having such an automatic engine stop function, whereby a lower limit is set on the amount of charge in the battery, and whereby a decision is made as to whether engine automatic stopping will be enabled to be applied (when the necessary conditions are satisfied), based upon that lower limit value.
For example as disclosed in Japanese patent application publication No. 2002-165775, such a system is provided having the following features. Following completion of each engine start, successive values of charge and discharge current to/from the battery are measured and are integrated with respect to time (discharge currents being negative values). Successive values of a charging current integral, i.e., net amount of charge supplied to the battery, are thereby obtained. If the predicted charging current integral at the current point in time is negative, indicating a net amount of discharge has occurred since completion of the preceding engine start, then the engine automatic stop control function is inhibited, whereas that function is enabled so long as the predicted charging current integral is positive.
Hence, the amount of charge remaining in the battery at completion of an engine start operation is set as the lower limit value of battery charge, for the purpose of determining whether to enable or disable the automatic engine stop function.
It is desirable that automatic engine stopping be performed (whenever the necessary conditions are satisfied) as frequently as possible, in order to minimize fuel consumption, i.e., it is desirable that inhibiting of automatic engine stop control should be applied as infrequently as possible.
It is therefore an objective of the present invention to provide a vehicle engine control system having an automatic engine stop control function, whereby the frequency of inhibiting that function (i.e., inhibiting for preventing excessive lowering of the stored charge in the battery) can be reduced by comparison with the prior art, without significantly shortening the operating lifetime of the battery.